The present invention claims priority to Japanese Patent Document No. P2000-301409 filed on Sep. 29, 2000 and Japanese Patent Document No. P2001-012207 filed Jan. 19, 2001. The above-referenced Japanese Patent Documents are hereby incorporated by reference to the extent permitted by law.
The present invention relates to a fuel cell and a method for the preparation thereof.
A need exists for a substitute or alternative clean and economical energy source which may take the place of, for example, fossil fuels, such as petroleum. For example, a hydrogen gas fuel is regarded as a desirable and alternative source of energy.
In this regard, hydrogen has a large amount of energy contained per unit weight and, in use, does not emit noxious gases or gases contributing to global warming. Thus, hydrogen can be utilized as an ideal energy source which is clean and moreover plentiful in supply.
In general, fuel cells have been developed which utilize hydrogen. In general, a fuel cell is capable of recovering an electrical energy from the hydrogen energy. Research and development in this field is continually advancing. It is expected that fuel cells can be made for application in large scale power generation or on-site self-generation of power, as a power source for an electric vehicle or the like.
The fuel cell, in general, includes a fuel electrode, such as a hydrogen electrode, and an oxygen electrode, arranged on both sides of a proton conductor film. By supplying fuel (hydrogen) and oxygen to these electrodes, a cell reaction occurs resulting in an electromotive force. In preparing the fuel cell, the proton conductor film, fuel electrode and the oxygen electrode are routinely molded separately and bonded together.
However, in forming the fuel electrode and the oxygen electrode separately, a variety of inconveniences can arise due to difficulties encountered in handling and general processing regarding same.
For example, if the strength of the fuel electrode or the oxygen electrode is taken into consideration, a certain thickness, for example, a thickness on the order of 100 xcexcm or more, may be needed. However, if the electrode thickness becomes too large, the cell reaction is lowered in efficiency, thus lowering the cell performance.
On the other hand, as the electrode thickness is decreased, the proton conductor film may be handled with difficulty due to its size decreased, to compensate for a decreased electrode thickness, as a fuel cell component separate and apart from the electrodes. Thus, the production of the fuel cell is lowered significantly.
It is therefore an advantage of the present invention to provide a fuel cell which is easy to manufacture and superior in cell performance, and a method for the preparation of the fuel cell.
Applicants have conducted a variety of research and experiments, and found that layers of a catalyst having a metal component may be effectively used to facilitate the performance of a fuel cell and/or as an oxygen cell.
In this regard, the fuel cell of the present invention can include a layer of a metal catalyst formed on a surface of a proton conductor film which operates or functions as a fuel electrode and/or as an oxygen electrode.
According to the present invention, the metal catalyst layer operates as a fuel electrode and/or as an oxygen electrode and is directly formed on the proton conductor film operating as a support. Thus, it is unnecessary to handle the fuel electrode and/or the oxygen electrode separately and thus take mechanical strength thereof into consideration when manufacturing the fuel cell of the present invention. Consequently, the fuel and oxygen electrodes can be increasingly reduced in thickness such that the cell reaction may proceed efficiently to improve the cell performance as well as the energy density of the fuel cell.
Moreover, in the present invention, the metal catalyst layer in an embodiment can include ventilation openings for supplying the fuel or oxygen gases. By the metal catalyst layer including the ventilation openings for supplying the fuel or oxygen gases, the cell reaction may proceed more efficiently, without obstructing the electrode reaction, thus further improving the cell performance.
Additionally, in an embodiment, the proton conductor film desirably exhibits thermal resistance. In this regard, it is desirable that the proton conductor film is formed by a matrix of a carbonaceous material mainly composed of carbon and into which proton dissociative groups are introduced.
In an embodiment, the present invention also relates to a method for the preparation of a fuel cell including forming a layer of a catalyst metal on a surface of a proton conductor film by one of sputtering, vacuum deposition, chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) or the like processes.
With the method for the preparation of a fuel cell, according to the present invention, electrodes of a fuel cell can be produced by a simplified technique which is based on a gas phase film-forming method.
With the method for the preparation of a fuel cell, according to an embodiment of the present invention, fine particles of a material different from the catalyst metal can be added, or dispersed or sprinkled onto the proton conductor film before forming the layer of the catalyst metal on a surface of the proton conductor film. In an embodiment, after forming the layer of the catalyst metal, the fine particles can be removed to form ventilation openings in the layer of the catalyst metal.
With the method for the preparation of a fuel cell, according to an embodiment of the present invention, the particle size of the fine particles is preferably larger than the thickness of the layer of the catalyst metal. By having the particle size of the fine particles larger than the thickness of the layer of the catalyst metal, ventilation openings can be formed more reliably in the layer of the catalyst metal.
In an embodiment, fine particles of silica are preferably used. In this case, silica powders added by dispersing, sprinkling or the like, on the surface of the proton conductor film can be effectively removed by ion milling or etching employing a fluorine-containing solution or a fluorine-containing gas or other like process.
It should be appreciated that the fine particles can include a variety of different and suitable materials. For example, in an embodiment, fine particles of tin oxide may also be used. In this case, tin oxide powders are added to the surface of the proton conductor film and can be effectively removed by ion milling, etching employing a fluorine-containing solution or a fluorine-containing gas or the like similar to fine particles of silica.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Invention and the Figures.